1. Field of the Invention
The present invention relates to an optical unit projecting a picture on a screen using a light source and picture display device and to a projection display apparatus and an imaging apparatus that have the optical unit.
2. Description of the Related Art
In a projection display apparatus (that is, a projector), a DMD (Digital Micromirror Device), which is one of micromirror picture display devices, is attracting attention as a picture display device capable of achieving a small and high luminance optical unit. The DMD performs optical modulation by individually controlling the angle of a micromirror provided for each pixel to divide DMD incident light into a direction (ON light) in which the light is incident on a projection lens and a direction (OFF light) in which the light is not incident on the projection lens.
In an optical system including an optical unit using the DMD, the main optical axis of incident light needs to be slanted at a predetermined amount with respect to the surface normal of the DMD so that the main optical axis of DMD reflected light is not aligned with the main optical axis of DMD incident light. When the rotational angle is slanted at +θ when the DMD is on or at −θ when the DMD is off, the DMD incident light is generally slanted at 2θ with respect to the center optical axis (surface normal) of the DMD. In addition, the spread angle is generally limited to an angle equivalent to θ or less by increasing the F-number of an illumination light beam incident on the DMD mirror (that is, by suppressing the spread of the illumination light beam) to prevent the contrast from being reduced by an overlap among an ON light beam, an OFF light beam, and flat light beam, which is a reflected light beam reflected by the surface of the cover glass covering the mirror device.